1. Field of the Invention
The present invention relates to a method of producing such a gallium nitride semiconductor light emitting device.
2. Description of the Related Art
Gallium nitride has higher forbidden band energy than conventional compound semiconductors such as indium phosphide and gallium arsenide. Thus, it is expected that a semiconductor expressed by general formula In.sub.x Al.sub.y Ga.sub.1-x-y N (0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.x+y.ltoreq.1) (hereinafter referred to as gallium nitride semiconductor) will be applied to a light emitting device which emits light with a wavelength from green to ultra violet, in particular, to a semiconductor laser device (hereinafter simply referred to as laser device).
In a conventional crystal-growing process for a gallium nitride semiconductor, after an undoped gallium nitride layer or a silicon-doped n-type gallium nitride layer is formed on a substrate, at least one gallium nitride semiconductor layer is formed on the semiconductor layer (by S. Nakamura et al, "Extended Abstracts of 1996 International Conference on Solid State Devices and Materials, Yokohama, 1996, pp. 67-69).
FIG. 2 is a sectional view showing an outlined structure of a gallium nitride laser device composed of a semiconductor layer formed by such a conventional crystal growing method.
In FIG. 2, the gallium nitride laser device is fabricated by forming on a (11-20) surface of a sapphire substrate 101 a 300 angstrom thick undoped gallium nitride low temperature growing buffer layer 102, a 3 .mu.m thick silicon-doped n-type gallium nitride contact layer 103, a 0.1 .mu.m thick silicon-doped n-type In.sub.0.05 Ga.sub.0.095 N crack protecting layer 104, a 0.4 .mu.m thick n-type Al.sub.0.07 Ga.sub.0.93 N clad layer 105, a 0.1 .mu.m thick silicon-doped n-type gallium nitride optical guide layer 106, a seventh period multiple quantum well structural activation layer 107 (composed of a 25 angstrom thick undoped In.sub.0.2 Ga.sub.0.8 N quantum well layer and a 50 angstrom thick undoped In.sub.0.05 Ga.sub.0.95 N barrier layer), a 200 angstrom thick magnesium-doped p-type Al.sub.0.2 Ga.sub.0.8 N indium dissociation protecting layer 108, a 0.1 .mu.m thick magnesium-doped p-type gallium nitride optical guide layer 109, a 0.4 .mu.m thick magnesium-doped p-type Al.sub.0.07 Ga.sub.0.93 N clad layer 110, a 0.2 .mu.m thick magnesium-doped p-type gallium nitride contact layer 111, a p-type electrode 112 (composed of nickel (first layer) and gold (second layer)), and an n-type electrode 113 (composed of titanium (first layer) and aluminum (second layer)).
In the gallium nitride laser device composed of semiconductor layers formed by the conventional crystal growing method shown in FIG. 2, the silicon-doped n-type gallium nitride layer is formed on the gallium nitride low temperature buffer layer 102. Generally, the crystalline characteristics of the silicon-doped Al.sub.x Ga.sub.1-x N (where 0.ltoreq.x.ltoreq.1) layer are inferior to the crystalline characteristics of the undoped Al.sub.x Ga.sub.1-x N (where 0.ltoreq.x.ltoreq.1) layer or the magnesium-doped Al.sub.x Ga.sub.1-x N (0.ltoreq.x.ltoreq.1) layer in half width at half maximum (FWHM) on a rocking curve in a two-crystal X-ray diffraction evaluation. Thus, the crystalline characteristics of each layer including the multiple quantum well activation layer 107 formed on the silicon-doped Al.sub.x Ga.sub.1-x N (where 0.ltoreq.x.ltoreq.1) layer deteriorate.